As nano-biotechnology was developed rapidly in recent years, artificially synthesized nano-particles with unique structures and functions have taken an increasingly important role in the biomedical field, including targeted drug delivery, high-resolution tumor imaging, and disease diagnosis, etc., and in other fields, such as protein purification, biochemical analysis, food safety, and environmental monitoring, etc. The measurement of size distribution of functional nano-particles is of great importance for quality control and actual application of nano-particles. In addition, there are various biological nano-particles in the natural world, such as bacteria, viruses, organelles, molecular assemblies, etc. Quick and high-resolution nano-particle detection techniques will provide powerful analytical means for pathogen identification, quality control of viral vaccines, measurement of transduction efficiency of gene transfer viral vectors, and research of basic life science.
Nano-particles can be analyzed effectively by means of high-sensitivity flow cytometry. For example, in some literatures (Anal. Chem. 2009, 81, 2555-2563 and J. Am. Chem. Soc. 2010, 132, 12176-12178), a technical solution of high-sensitivity flow cytometry is disclosed, comprising: compressing a sample liquid to be detected into a sample liquid flow by hydrodynamic focusing with a sheath fluid, and irradiating measuring light to the sample liquid flow, wherein the volume of the sample liquid flow subjected to the irradiation of the measuring light is approx. 800 fL and 150 fL; collecting the scattered light and/or fluorescent light emitted from the nano-particles in the sample liquid flow via an aspheric lens and obtaining signals, and analyzing the nano-particles according to the signals. However, the technical solution disclosed in the technical literatures can only detect polystyrene nano-particles in particle size greater than 100 nm, but can't detect smaller nano-particles with lower-refractivity. For nano-particles, the intensity of scattered light is attenuated at a rate proportional to sixth-power of particle size, i.e. when the particle size is halved, the signal strength will be decreased by 64 times. Therefore, it is difficult to detect nano-particles with smaller particle size.